Why are flexible solar panels catching fire?

[Cpt Pat]

Originally Posted by a64pilot

With the house panels that catch fire it’s almost always because there are flammable materials that build up under the panels, leaves etc.
There have been many panel failures that don’t amount to anything except a failed panel because there was nothing to burn.

When I was in Georgetown last Winter there were three panel failures and small fires, and a forth the guy was sailing came up from a short break from down below and his Bimini was on fire, he lost his boat I believe.
My take is don’t mount any kind of panel on something that will burn, but your boat, you do as you think best.

Do you mean the ignition starts because of the build up of flammable materials - or that it spreads because of those materials?

If you mean it starts because of those materials, then, unless you have materials with an extremely low ignition temperature, I doubt panels that haven't malfunctioned are capable of getting hot enough to ignite anything.

In direct sunlight, at noon, my flat "flexible" panels don't exceed 130 degrees F at the hottest point on their surface (measures with a Fluke IR thermometer). There are very few materials that can ignite at that temperature. I assume no one is stuffing nitrocellulose under their panels.

https://www.engineeringtoolbox.com/fuels-ignition-temperatures-d_171.html

Failed panels are bad enough. Failed panels that can possibly, under any circumstance, set anything on fire are completely unacceptable on a boat. I can't think of encountering anything that is worse on a boat than fire.

[Cadence]

Originally Posted by Cpt Pat

It's usually a single point on the flexible panels that catches fire. It looks like someone burned a spot by concentrating sunlight with a magnifying glass. That's where the bonding wire fractured from fatigue failure. After that, the burn spot starts to grow.


So it's not a ventilation issue, which would affect a large area of the panel.


Of course, ventilation is beneficial for all panels. The panel output decreases with rising temperature. But ventilation isn't a fire safety issue - only a performance issue.


BTW, if you want to hang a conventional framed panel, it's just as important to attach reinforcement to the back of the panel frame to prevent twisting (racking). Framed panels are also intended to be mounted on a rigid surface. I used aluminum bar stock.

Remember using a magnifying glass to start a fire as a boy scout? I guess mounting a flexible panel on cloth Bimini top would be about the same with a failure at one point in the panel. I doubt the panels ambient temp. would be a problem.

[Cpt Pat]

Originally Posted by Cadence

Remember using a magnifying glass to start a fire as a boy scout? I guess mounting a flexible panel on cloth Bimini top would be about the same with a failure at one point in the panel. I doubt the panels ambient temp. would be a problem.

Provided the panel had any capability to concentrate light. Which is doesn't. The pinpoint nature of the panel failures is due to fractured intra-cell bonding wires, creating high resistance that dissipates power as heat. Aluminum bonding wires have a limited flex life. Then coat the whole panel with a flammable plastic, and you have a time-bomb.

Substituting aluminum with gallium-based alloys that stay fluid at room temperatures could possibly solve the flexure-failure problem. But I'm not a panel maker. I'll wait for them to figure it out. I use rigid panels.

[a64pilot]

Originally Posted by Cpt Pat

Do you mean the ignition starts because of the build up of flammable materials

Panels can apparently sometimes develop hot spots and burn through. My assumption is a short, but that’s my assumption.
They seem to self extinguish though, unless there is flammable material in contact with them, then there can be a fire.
At least thats my take on it.
Hard panels don’t seem to be immune either as I assume not many flexible panels are mounted on a house, and there have been house fires, maybe all wiring?
All boat fires from panels that I know of were flexible panels though and all on Bimini’s. I don’t think they could get fiberglass going, but again that is my opinion, not fact.
As I said there were four in Georgetown this year, and one guy became quite the expert and was on the net a couple of times. I remember hearing him after the boat that was sailing burnt.

[LittleWing77]

Capt'n Pat, you are amazing! Thank you so much for walking us through it.

Gratefully,
LittleWing77

[zeehag]

my flexible panels pasted more than 5 yrs. constantly in sun or whatever was overhead in san diego.
flexible panels have a barrier containing the cells. unless you remove the cells from the barrier, which was impossible in the ones i had, there is no issue. i had some of my panels on a dodger and some in cockpit. i had total of 5 of the flexible solar panels sold by solar electric inc, now out of business.
no issue.
perhaps it is the installation or the panel itself being defective.....
best o luck.

[OceanPlanet]

I see a bit of confusion here about what causes hot spots and fires on flexible solar panels.

In any electrical circuit, if there is resistance in any part of the circuit to the flow of current from a power source, it can create heat. Unless the circuit is opened entirety (breaking the path between positive & negative).

Any crack or fracture in any cell in a solar panel or in the conductors attached to them, will create resistance to the flow of current across the cell or conductor. Until or unless the circuit is entirely open (for instance by disconnecting the panel from the controller & battery) current produced by the panel will try to flow across the bad connection (crack or fracture) which creates heat.

Panels with metal backing or mounted on a deck (that haven't been already damaged before installation) or panels with cells designed with extra pathways around cracks & fractures, will much less chance of getting hot spots.

High quality flexible panels with the proper cells and construction are perfectly fine when properly installed on canvas surfaces. This means using cells that weren't fractured to begin with, panels that have been handled carefully, and that the panels are not crossing over support bars under canvas, etc.

If the cells DO get cracked, then you want to have cells like the Merlin (SR version of Solbian) that are designed to have alternative pathways for current to flow around most such fractures.

I hope this is helpful info

[Lost Horizons]

Originally Posted by MV Wanderlust

There have been a few reports of flexible solar panels burning, melting, or even catching fire. Can someone please explain from a physics or engineering standpoint how this happens?

To help visualizing it, imaging that a solar panel is a huge magnifying glass that converts 20% of incoming photons into electrons and sends them to a battery through an electric circuit. If the circuit is damaged its electrical resistance may locally increase causing a voltage drop where a portion of the electrical energy is then converted to heat, like in electric heater. So here you have a huge magnifying glass focusing sun’s energy in a spot. When the size of the spot is small, it will start smoking. This may happen regardless of a brand name or panel construction type as long as a bottle neck for the energy flaw appears.

[Perna]

I am not an expert but as I understand it there is a major difference between domestic roof top type systems and 12/24 V marine systems. Basically most domestic systems consist of several panels connected in series giving more than 80V and that is the voltage where a continuous DC arc can and will occur if there is a break in the wiring when the current is flowing.

Here's a very impressive demonstration of DC arcs.

Solar fires

This means that domestic systems are far more dangerous than lower voltage marine set ups.

[nilespf]

Originally Posted by MV Wanderlust

A friend is considering a boat that has a bimini top. He would like to install solar and the best/only option would be flexible solar panels on the bimini.

There have been a few reports of flexible solar panels burning, melting, or even catching fire. Can someone please explain from a physics or engineering standpoint how this happens? Can it be prevented or is it just an inherent tradeoff for flexibility?

Thanks.

John

From and engineering point the reason a panel burns is because a high enough localized resistance develops in the current path of the solar panel. This high resistance may form due a number of reasons--let your imagine run wild.


Manufacturers have begun to install bypass diodes to mitigate the effect of hot spots. A hot spot i.e. the resulting localized rise of surface temperature (of the medium the PV cell is mounted to) due to the inability of a PV cell to either produce current or properly pass current. The cells series resistance can rise due to infant mortality, quality issues, partial shading, substrate mounting breakdown and often in the case of flex panels a loosening of external connections or breaking of internal current paths due to constant flexing.



Bypass diodes come with added cost so manufacturers have chosen to protect a string of PV cells e.g. a 60 cell array may have 6 bypass diodes grouped in strings of 10 PV cells. Without going into a bunch of description how the bypass diodes are connected together if a flex or any type of panel happens to develop a hot spot (within the string of diodes the bypass diode is protecting) the bypass diode will bypass the current around the hot spot. If a hot spot occurs anywhere out side the circuit of the bypass diode were in trouble. e.g. main connections going in or out.


A soldering iron is nothing other than a temperature tolerant resistor with enough current going though it to raise the temperature. The flex panels unfortunately can be mounted on a surface that is not temp tolerant in that the panel stays together long enough (continues to pass current) after the mounting surface reaches ignition temperature.


Personally, if assured that Flex panel substrates can last as long as the stiff panels including UV degradation effects and a independent investigation could pigeon hole why the hot spots occur, I would have no problem using on a Bimini. But I haven't seen it.

[secrabtree]

The flexable solar panels do not last as long and are a little more difficult to keep clean. When I had my Cal 39 I had a few bars added to the bimini so that I could mount 4 - 160W solar pannels. No more need for a new cloth bimini cover every couple years because the solar panels became my new bimini cover. Worked fine.

[nilespf]

Originally Posted by secrabtree

The flexable solar panels do not last as long and are a little more difficult to keep clean. When I had my Cal 39 I had a few bars added to the bimini so that I could mount 4 - 160W solar pannels. No more need for a new cloth bimini cover every couple years because the solar panels became my new bimini cover. Worked fine.

The only room I have is the Bimini but couldn't bring myself to put flex up.

[secrabtree]

Originally Posted by nilespf

The only room I have is the Bimini but couldn't bring myself to put flex up.

Niles -My "Bimini" WAS four rigid non-flexible 160W solar panels mounted on a modified bimini frame of 1" diameter stainless steel tubing.

[jsanton]

I replaced my Bimini fabric with 1/4” starboard. Needed some stiffeners. Mounted flexible panels to that. It’s not flat, but is rigid. That’s what flexible solar panels are designed for.

[tjandoverguy]

What kind of material is that star board